Of particular interest to the present application are drives for belt-driven, rigid baseplate, magnetic tape mini-cartridges commonly used in the personal computer industry for data storage. In general, these mini-cartridges have evolved from a data cartridge design that was first introduced for use in the computer industry by the Minnesota Mining and Manufacturing Company (3M) in the early 1970's (U.S. Pat. No. 3,692,255, issued to Robert A. Von Behren in 1972). The belt driven magnetic data cartridges introduced by 3M in the early 1970's were approximately 100 mm by 150 mm and the magnetic tape was 6.35 mm (0.250 inches) wide. Cartridges of that size and corresponding drive mechanisms are still commercially available. In 1976, smaller mini-cartridges were developed, as described by Alan J. Richards, Mini Data Cartridge: A Convincing Alternative for Low-Cost, Removable Storage, Hewlett-Packard Journal, May, 1976. The mini-cartridge size is 63.5 mm by 82.5 mm. Versions of the mini-cartridge are commercially available from a variety of vendors with tape widths varying from 3.81 mm (0.150 inches) to 8.00 mm (0.315 inches).
Recently, 3M has introduced improved mini-cartridges with increased data capacity. The new mini-cartridges are larger than the mini-cartridges described above. There is a need for drives that can accommodate both the old and new tape mini-cartridges.
FIG. 1 is a top view of a mini-cartridge 100. The mini-cartridge has an alignment slot 108 along each side for guidance of the mini-cartridge during insertion into the drive. Typically, a corresponding drive has fixed guide rails that match the slots 108. In the older mini-cartridges, the cartridge slots 108 extend to point 112. The new mini-cartridges have a front surface that is identical in size to the older mini-cartridges. However, rear surfaces of the new mini-cartridges (indicated by dashed line 114) have been enlarged to permit more tape. In the new mini-cartridges, the slots 108 only extend to point 116. Therefore, the length of the drive guide rails for new mini-cartridges must be shorter than the length of the drive guide rails previously used for older mini-cartridges.
The front surface of the mini-cartridge has a door 102 (illustrated as partially open). When the door is closed, the internal magnetic tape in the mini-cartridge is protected from exposure to dust or contact with external objects. When the door 102 is open, the tape is exposed for contact with a magnetic head in the drive. The door 102 pivots around a pivot point 104 and has an extension 106 that extends beyond the pivot point. Typically, for older mini-cartridges, as the mini-cartridge is inserted into the drive, a fixed guide rail in the drive first contacts the extension 106, opening the door 102. If the length of the drive guide rail is made shorter for new mini-cartridges as discussed above, the mini-cartridge must be inserted further into the drive before the drive guide rail first makes contact with extension 106. The dimensions are such that short fixed drive guide rails cannot be used to open the door 102 because with short rails, the door cannot open completely before striking the magnetic head or other drive chassis features. Therefore, there is need for a new cartridge door opening apparatus that works with both old and new mini-cartridges.
One proposed mechanism uses a spring loaded plunger. The tip of the plunger makes contact with the extension 106 early during mini-cartridge insertion. The spring force is greater than the force required to open the door 102. When the end 116 of the slot 108 of a new mini-cartridge reaches the tip of the plunger, the end of the slot forces the plunger to retract. The plunger therefore opens the door and then retracts rearward out of the way. However, because of the curved surface at the end of the slot 108, a lateral force is placed on the plunger tending to cause the plunger to be wedged between the mini-cartridge and the chassis, resulting in excessive wear and binding of the plunger. An improved mechanism is needed that eliminates contact with the curved surface of the slot.